The Council of Trent on Justification
HOW THE GRATUITOUS JUSTIFICATION OF THE SINNER BY FAITH IS TO BE UNDERSTOOD
But when the Apostle says that man is justified by faith and freely, these words are to be understood in that sense in which the uninterrupted unanimity of the Catholic Church has held and expressed them, namely, that we are therefore said to be justified by faith, because faith is the beginning of human salvation, the foundation and root of all justification, without which it is impossible to please God and to come to the fellowship of His sons; and we are therefore said to be justified gratuitously, because none of those things that precede justification, whether faith or works, merit the grace of justification.
For, if by grace, it is not now by works, otherwise, as the Apostle says, grace is no more grace.
Canons Concerning Justification
If anyone says that man can be justified before God by his own works, whether done by his own natural powers or through the teaching of the law, without divine grace through Jesus Christ, let him be anathema.
If anyone says that divine grace through Christ Jesus is given for this only, that man may be able more easily to live justly and to merit eternal life, as if by free will without grace he is able to do both, though with hardship and difficulty, let him be anathema.
If anyone says that without the predisposing inspiration of the Holy Ghost and without His help, man can believe, hope, love or be repentant as he ought, so that the grace of justification may be bestowed upon him, let him be anathema.
If anyone says that man’s free will moved and aroused by God, by assenting to God’s call and action, in no way cooperates toward disposing and preparing itself to obtain the grace of justification, that it cannot refuse its assent if it wishes, but that, as something inanimate, it does nothing whatever and is merely passive, let him be anathema.
Full context with footnotes and scriptural references at this link: